Process for preparing substituted N-phenylhydroxylamines

Abstract

The present invention relates to a process for the preparation of a ring-substituted N-phenylhydroxylamine by reduction of the correspondingly substituted nitrobenzene compound, wherein the reduction is carried out by reacting the substituted nitrobenzene compound with hydrazine in the presence of a ruthenium catalyst.

We claim: 
     
       1. A process for preparing a substituted N-phenylhydroxylamine by reduction of corresponding substituted nitrobenzene compound, wherein the reduction is carried out by reacting the substituted nitrobenzene compound with hydrazine in the presence of a ruthenium catalyst. 
     
     
       2. The process as claimed in  claim 1 , wherein the substituted N-phenylhydroxylamine carries at least one substituent in the ortho-position relative to the hydroxylamine group. 
     
     
       3. The process as claimed in  claim 2 , wherein the substituted N-phenylhydroxylamine is a compound of the formula (I), 
       
         
           
           
               
               
           
         
         wherein 
         R 1  is selected from the group consisting of halogen, cyano, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, C 1 -C 4 -alkoxy, C 1 -C 4 -haloalkoxy, C 1 -C 4 -alkylcarbonyl, CO 2 H, CONH 2 , C 1 -C 4 -alkylaminocarbonyl, di-(C 1 -C 4 -alkyl)aminocarbonyl, C 1 -C 4 -alkylcarbonylamino, C 1 -C 4 -alkoxycarbonyl, and a group A-B, wherein
 A is —O—, —CH 2 —, —O—CH 2 —, —CH 2 —O—, —CH 2 —O—CO—, —CH═CH—, or a single bond, and 
 B is phenyl, naphthyl, pyridinyl, pyrazinyl, pyrimidinyl, pyridazinyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, 1,2,4-triazolyl, 1,2,3-triazolyl, furanyl, thienyl, pyrrolyl or C 3 -C 7 -cycloalkyl, wherein B may be unsubstituted or may carry 1 to 3 substituents R e ; 
 R e  is cyano, halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, C 1 -C 4 -alkoxy, C 1 -C 4 -haloalkoxy, C 1 -C 4 -alkylthio, C 1 -C 4 -alkylcarbonyl, C 1 -C 4 -alkoxycarbonyl, CO 2 H, CONH 2 , C 1 -C 4 -alkylaminocarbonyl, di-(C 1 -C 4 -alkyl)aminocarbonyl, C 1 -C 4 -alkylcarbonylamino, or phenyl which may be unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from the group consisting of halogen, C 1 -C 4 -alkyl and C 1 -C 4 -haloalkyl; 
 
         R 2  is selected from the group consisting of halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, C 1 -C 4 -alkoxy, C 1 -C 4 -haloalkoxy and C 1 -C 4 -alkoxycarbonyl; and 
         n is 0, 1, 2 or 3. 
       
     
     
       4. The process as claimed in  claim 3 , wherein
 R 1  is selected from the group consisting of halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, and a group A-B. 
 
     
     
       5. The process as claimed in  claim 3 , wherein the substituted N-phenylhydroxylamine I is a compound of the formula (I′), 
       
         
           
           
               
               
           
         
         wherein 
         R e1  is hydrogen or phenyl which may be unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from halogen and C 1 -C 4 -alkyl, 
         R e2  is halogen, C 1 -C 4 -alkyl and C 1 -C 4 -haloalkyl, 
         m is 0 or 1. 
       
     
     
       6. The process as claimed in  claim 1 , wherein the catalyst is a supported catalyst comprising ruthenium which is supported on an inert support material. 
     
     
       7. The process as claimed in  claim 6 , wherein the support material is selected from the group consisting of carbon, alumina and silica. 
     
     
       8. The process as claimed in  claim 6 , wherein the catalyst has a ruthenium content of 0.1 to 10 percent by weight, based on the total weight of the catalyst. 
     
     
       9. The process as claimed in  claim 8 , wherein the catalyst has a ruthenium content of about 2 to 7 percent by weight, based on the total weight of the catalyst. 
     
     
       10. The process as claimed in  claim 1 , wherein the catalyst has a weight average particle size of 20 to 200 μm. 
     
     
       11. The process as claimed in  claim 1 , wherein the catalyst is employed in an amount of 10 −4  to 10 −2  mol ruthenium, based on 1 mol of the substituted nitrobenzene compound. 
     
     
       12. The process as claimed in  claim 1 , wherein a catalyst is employed which has been activated by treatment with hydrogen. 
     
     
       13. The process as claimed in  claim 1 , wherein the hydrazine is employed in an amount of 1.1 to 5.5 mol per 1 mol of the substituted nitrobenzene compound used. 
     
     
       14. The process as claimed in  claim 1 , wherein the concentration of the substituted nitrobenzene compound in the total reaction mixture is in the range of 8.0 to 25.0% (w/w). 
     
     
       15. The process as claimed in  claim 1 , wherein the reduction is carried out in an aprotic organic solvent.